Phoenician taw — "mark", through Greek tau.
T
taw was the last letter of the Phoenician alphabet and it was drawn as a cross — the mark someone who could not write put instead of a signature.
Armstrong · Baxter · Bennett · Brewster · Butler · Carpenter · Carter · Castillo · Conti · Contreras · Cortez · Cutler · Elliott · Esposito
In the modern alphabet this letter is number 20 of 26. Before it comes S, after it U. The order itself is inherited: Latin took it from Greek, Greek from Phoenician, and the sequence has survived largely unchanged for about three thousand years. Every rearrangement since has been an insertion, not a reshuffle.
This is a consonant: it sets the hardness of a name and how it meets the next word. In a corpus of 315 surnames this letter opens 8 and closes 12. Among the 96 given names in the base it appears in 23. The surname carrying the most of it is Bennett, with 2.
Robert · Thomas · Christopher · Matthew · Anthony · Steven · Timothy · Patrick · Peter · Nathan · Arthur · Ethan
These letters came from the Greek alphabet.